Collagen has been used as an implantable biomaterial for more than 50 years. The collagen used for biomedical implants is either derived from animals (e.g., cows, pigs, horses) and humans, or it is manufactured in vitro using recombinant engineering. It is known to be biocompatible and is resorbed and remodeled like natural tissues, via cellular and enzymatic processes.
Conventional collagen implants typically have been made of highly porous, reconstituted bovine (i.e., cow) collagen. These collagen implants are commercially sold to surgeons as rectilinear sheets with uniform thicknesses and porosity. Their low density and high porosity make these collagen membranes supple and conformable. Unfortunately they therefore have inadequate tensile strength and stiffness, particularly after wetting with saline or blood, for use as a containment device in surgical applications.
Bone is the body's primarily structural tissue; consequently it can fracture and biomechanically fail. Fortunately, it has a remarkable ability to regenerate because bone tissue contains stem cells which are stimulated to form new bone within bone tissue and adjacent to the existing bone. Boney defects regenerate from stem cells residing in viable bone, stimulated by signally proteins, and multiplying on existing cells or on an extracellular matrix (i.e., trellis). Like all tissues, bone requires support via the vascular system to supply nutrients and cells, and to remove waste. Bone will not regenerate without prompt regeneration of new blood vessels (i.e., neovascularization), typically with the first days and weeks of the regenerative cascade.
After tooth loss, the adjacent jawbone (maxilla or mandible) frequently resorbs or atrophies. This may cause problems when it is desired to replace a missing tooth with a dental implant because the required depth of bone needed to adequately support the implant may not be present. Thus, prior to implanting a dental implant, it is often necessary for the oral surgeon to regenerate the adjacent bone to at least the minimum depth to provide adequate osteointegration of the dental implant. A common procedure for this purpose is alveolar ridge augmentation.
Various attempts have been made in the past to stimulate or augment bone regeneration by introducing a bone regenerating material proximate a deteriorated bone structure. Such efforts have met with limited success, however, because they have not been able adequately to control the placement of the bone regenerating material and thus guide the development of new or additional bone. Bone regenerating materials are classified as “bioactive” because they are biocompatible and stimulate new bone formation. Examples of bioactive materials are autograft, osteogenic stem cells, osteoinductive proteins, and osteoconductive matrices. Bioactive agents are typically delivered to the operative site by the surgeon as deformable, flowable biomaterials. The predictability of bioactive agents is poor, however because it is difficult to adequately control the placement of the bone regenerating material and thus guide the development of new or additional bone. Liquids, gels, granules, composites can be easily injected from syringes, but they can also go to unintended locations causing severe complications. Moreover, bioactive materials often migrate over time from the desired site. Measures undertaken to control the placement of the bone regenerating material may hinder cell ingrowth and formation of blood vessels needed for development of additional bone and thus impede the desired bone regeneration.
In alveolar ridge augmentation of atrophied jawbones to provide sufficient bone depth to facilitate stable implantation of a dental implant, a principal difficulty is the maintenance of the desired ridge shape, both as to height and as to width. While many answers exist for horizontal grafting, there are very few constructs to facilitate vertical grafting. In the past, bone graft material containment members constructed of titanium mesh have been used to address this problem. Titanium mesh is used because it has the requisite structural strength and integrity to provide containment and yet does not induce adverse effects in proximate tissues. However, because of its long term stability, it is necessary to carry out a second surgery to remove the containment member after the bone graft has achieved the desired degree of osseointegration before a dental implant can be implanted in the augmented bone. This results in concomitant tissue damage and often further delays the installation of the dental implant while the tissues damaged during removal of the titanium mesh containment member heal.
Thus, despite considerable efforts of the prior art, there has remained a long felt need for better methods of bone regeneration, especially for alveolar ridge augmentation in preparation for the installation of dental implants.